As the advantages of fiber optic based communications and control of industrial processes become better known, increasing emphasis is being placed on using various methods of simple, inexpensive and reliable communication of low level radiant energy via fiber optics to the measurement site, making the desired measurement, and returning the measurement information on the fiber optic paths to the control location. Among the many problems facing designers are practical manufacturing techniques for ensuring precise registration of optical and mechanical elements in the transducers (or the like). Of especially critical importance is precise registration of the optical fiber or fibers and the object receiving or sending the radiant energy.
More particularly, the optical fiber of an optically based transducer may be terminated at a particular fixed position within the transducer, perpendicular to a moving surface of a member or element which moves in response to a process control measurand. Such members or elements may include resonant elements or structures or other moving surfaces. The goal may include measurement of displacements as small as one micron or less.
Current technology involves careful, time consuming alignment of the respective elements, which may be further aided by mechanical or electromechanical manipulation.
The present invention eliminates the need for such critical alignment by creating an optimally-located optical target on the mechanical structure after mechanical fabrication of the structure is complete.
For the purpose of this limited description, "process control" includes both individual variable processes and complex multivariable processes involving a large number of controlled process conditions characterizable as physical parameters or "measurands", such as fluid flow, flow rate, temperature, pressure, differential pressure, level, or the like. "Resonant element" or "resonant mechanical structure" as used herein generally refers to a beam, hollow-beam, cantilevered beam and cantilevered hollow beam, and doubleor other multiple-beam elements, and ribbon, wire or other articles of manufacture, and their equivalents, all of which can be resonated at particular oscillation frequencies. Specifically included are tuning fork structures of the single- and double-ended varieties, as well as multiple tine tuning fork structures. Also included are sensors which make analytical measurements through mass change, such as by members or coatings capable of adsorbing or absorbing entities being analyzed.
As used herein, the term "radiant energy" includes energy of a wavelength between 0.1 and 100 micrometers, and specifically includes infrared, ultraviolet, and visible light energy. For simplicity, such radiant energy may be referred to generally and without limitation as "light", "light energy", or "optical power". Such radiant energy may also be described as "steady" or "continuous" or "continuous wave" in order to distinguish it from radiant energy signals which are modified to carry information. The term "radiant energy" specifically includes coherent and incoherent light energy.
"Modulation" is used broadly herein. It is intended to mean modifying (or the modification) of some characteristic or characteristics of a light beam so that it varies in step with the instantaneous value of another signal, and specifically may be used herein to describe amplitude modulation and frequency modulation. The term "steady" radiant energy as used herein refers to radiant energy having a substantially constant intensity level (that is, absent short term variations in intensity) and having substantially unchanging spectral distribution.
"Fluid" includes gases and/or liquids. The term "force" is used to describe any physical parameter or phenomenon capable of moving a body or modifying its motion, and specifically includes force exerted per unit area (pressure) and any parameter or phenomenon capable of conversion to pressure.
The term "transducer" is used to describe a device to convert energy from one form to another, and as used herein, the terms "opto-electric transducer", "electro-optic transducer", "photo-kinetic transducer," and the like more specifically describe the class of devices useful for converting radiant energy to electrical energy and electrical energy to radiant energy, or radiant energy to kinetic energy. Note that conversion to an intermediate form of energy may occur in arriving at the objective form of energy in the conversion process.